Vaccines provide the best defense against infectious diseases and biological warfare agents particularly for many of the pathogens that enter the host through mucosal surfaces. We have developed an oral vaccine platform based in Lactobacilli, a group of bacteria "generally regarded as safe" by the FDA, that induces both systemic and mucosal immunity. In this RO1, we propose to expand our platform technology to develop an oral vaccine against a Category A, bacterial bioterrorism agent, Y. pestis, a highly lethal agent capable of inducing mass casualties. We will achieve this goal with the following aims: Specific Aim 1. Construct and characterize Lactobacillus spp. oral Y. pestis vaccine candidates. We will use the proven protective antigens, Low calcium response antigen V, (LcrV and rV10, LcrV modified to remove its immunosuppressive activity), and Fraction 1 (F1) as our vaccine antigens. Specific Aim 2. Screen for the best vaccine candidates and characterize the immune response to the vaccine. Orally immunize mice with Lactobacillus expressing recombinant LcrV and F1 and define their systemic and mucosal antibody responses to the vaccine antigen. Define the site of antigen entry and the nature of the cells involved in uptake and T cell activation. Evaluate cellular immune responses to the vaccine antigens in vitro. Specific Aim 3. Choose the most promising vaccine candidate or candidates and optimize them based on the knowledge gained in specific aim 2. Demonstrate vaccine efficacy against mucosal challenge with Y. pestis using the mouse nasal model of pneumonic plague. PUBLIC HEALTH RELEVANCE: Vaccines provide the best defense against infectious diseases and biological warfare agents particularly for many of the pathogens that enter the host through mucosal surfaces. We have developed an oral vaccine platform based in Lactobacilli, a group of bacteria "generally regarded as safe" by the FDA, that induces both systemic and mucosal immunity. In this RO1, we propose to expand our platform technology to develop an oral vaccine against a Category A, bacterial bioterrorism agent, Y. pestis, a highly lethal agent capable of inducing mass casualties.